| Message ID | 20211215000310.113753-1-connoro@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | bpf: fix panic due to oob in bpf_prog_test_run_skb | expand |
On Wed, Dec 15, 2021 at 12:03:10AM +0000, Connor O'Brien wrote: > From: Daniel Borkmann <daniel@iogearbox.net> > > commit 6e6fddc78323533be570873abb728b7e0ba7e024 upstream. > > sykzaller triggered several panics similar to the below: > > [...] > [ 248.851531] BUG: KASAN: use-after-free in _copy_to_user+0x5c/0x90 > [ 248.857656] Read of size 985 at addr ffff8808017ffff2 by task a.out/1425 > [...] > [ 248.865902] CPU: 1 PID: 1425 Comm: a.out Not tainted 4.18.0-rc4+ #13 > [ 248.865903] Hardware name: Supermicro SYS-5039MS-H12TRF/X11SSE-F, BIOS 2.1a 03/08/2018 > [ 248.865905] Call Trace: > [ 248.865910] dump_stack+0xd6/0x185 > [ 248.865911] ? show_regs_print_info+0xb/0xb > [ 248.865913] ? printk+0x9c/0xc3 > [ 248.865915] ? kmsg_dump_rewind_nolock+0xe4/0xe4 > [ 248.865919] print_address_description+0x6f/0x270 > [ 248.865920] kasan_report+0x25b/0x380 > [ 248.865922] ? _copy_to_user+0x5c/0x90 > [ 248.865924] check_memory_region+0x137/0x190 > [ 248.865925] kasan_check_read+0x11/0x20 > [ 248.865927] _copy_to_user+0x5c/0x90 > [ 248.865930] bpf_test_finish.isra.8+0x4f/0xc0 > [ 248.865932] bpf_prog_test_run_skb+0x6a0/0xba0 > [...] > > After scrubbing the BPF prog a bit from the noise, turns out it called > bpf_skb_change_head() for the lwt_xmit prog with headroom of 2. Nothing > wrong in that, however, this was run with repeat >> 0 in bpf_prog_test_run_skb() > and the same skb thus keeps changing until the pskb_expand_head() called > from skb_cow() keeps bailing out in atomic alloc context with -ENOMEM. > So upon return we'll basically have 0 headroom left yet blindly do the > __skb_push() of 14 bytes and keep copying data from there in bpf_test_finish() > out of bounds. Fix to check if we have enough headroom and if pskb_expand_head() > fails, bail out with error. > > Another bug independent of this fix (but related in triggering above) is > that BPF_PROG_TEST_RUN should be reworked to reset the skb/xdp buffer to > it's original state from input as otherwise repeating the same test in a > loop won't work for benchmarking when underlying input buffer is getting > changed by the prog each time and reused for the next run leading to > unexpected results. > > Fixes: 1cf1cae963c2 ("bpf: introduce BPF_PROG_TEST_RUN command") > Reported-by: syzbot+709412e651e55ed96498@syzkaller.appspotmail.com > Reported-by: syzbot+54f39d6ab58f39720a55@syzkaller.appspotmail.com > Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> > Signed-off-by: Alexei Starovoitov <ast@kernel.org> > [connoro: drop test_verifier.c changes not applicable to 4.14] > Signed-off-by: Connor O'Brien <connoro@google.com> > --- > Hello, > > This is a backport for the 4.14 stable tree. Now queued up, thanks. greg k-h
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 6be41a44d688..4f3c08583d8c 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -96,6 +96,7 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr, u32 size = kattr->test.data_size_in; u32 repeat = kattr->test.repeat; u32 retval, duration; + int hh_len = ETH_HLEN; struct sk_buff *skb; void *data; int ret; @@ -131,12 +132,22 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr, skb_reset_network_header(skb); if (is_l2) - __skb_push(skb, ETH_HLEN); + __skb_push(skb, hh_len); if (is_direct_pkt_access) bpf_compute_data_end(skb); retval = bpf_test_run(prog, skb, repeat, &duration); - if (!is_l2) - __skb_push(skb, ETH_HLEN); + if (!is_l2) { + if (skb_headroom(skb) < hh_len) { + int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb)); + + if (pskb_expand_head(skb, nhead, 0, GFP_USER)) { + kfree_skb(skb); + return -ENOMEM; + } + } + memset(__skb_push(skb, hh_len), 0, hh_len); + } + size = skb->len; /* bpf program can never convert linear skb to non-linear */ if (WARN_ON_ONCE(skb_is_nonlinear(skb))) diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index d4f611546fc0..0846345fe1e5 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -4334,6 +4334,24 @@ static struct bpf_test tests[] = { .result = ACCEPT, .prog_type = BPF_PROG_TYPE_LWT_XMIT, }, + { + "make headroom for LWT_XMIT", + .insns = { + BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), + BPF_MOV64_IMM(BPF_REG_2, 34), + BPF_MOV64_IMM(BPF_REG_3, 0), + BPF_EMIT_CALL(BPF_FUNC_skb_change_head), + /* split for s390 to succeed */ + BPF_MOV64_REG(BPF_REG_1, BPF_REG_6), + BPF_MOV64_IMM(BPF_REG_2, 42), + BPF_MOV64_IMM(BPF_REG_3, 0), + BPF_EMIT_CALL(BPF_FUNC_skb_change_head), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + .prog_type = BPF_PROG_TYPE_LWT_XMIT, + }, { "invalid access of tc_classid for LWT_IN", .insns = {